Please join the Department of Biological Sciences for the thesis defense of biological sciences master’s student Roxanne Beltran. Beltran joined the program in fall 2013 and has played an integral role in the NSF-funded research project, “The Cost of a New Fur Coat: Interactions between reproduction and molt in Weddell Seals in Erebus Bay, Antarctica,” under Drs. Jennifer Burns and J. Ward Testa. To learn more about Roxanne and her work with the ‘B-292’ research team, aka “Seal Team Six,” please visit the team’s website.
One of the crucial scientific challenges of this century is characterizing the vulnerability of ecosystems to global change. Bioenergetic models, which estimate total energy requirements by extrapolating simple physiological calculations to population-level metrics, can provide a theoretical construct for addressing specific physiological and ecological questions about how animals balance energy intake with expenditure. However, these linear models fail to link energy deficiencies with reproductive consequences or consider behavioral plasticity, and thus cannot be used to predict population-level consequences of environmental changes. An alternative approach is to use agent-based models, which can accommodate dynamic associations between physiological processes, utilize empirical weather data, permit unique and variable individuals to interact with extrinsic conditions, link energy deficiencies to reproductive consequences and allow individuals to alter their behaviors.
Here, I present an agent-based, ecophysiological model that simulates the energy balance of adult, female Weddell seals (Leptonychotes weddellii). The inputs include physiological parameters and population-wide ranges for the duration and phenology of life history events such as lactation and molt. Energy intake depends on foraging effort and stochastic prey availability at each timestep, whereas energy expenditure is calculated from time- and behavior-specific demands. The simulated animal selects an activity (forage, nurse pup, molt, rest), based on body condition, life history constraints (i.e. dependent pup), and extrinsic conditions (e.g. air/water temperature, wind speed). At the end of each timestep, the energy budget is balanced and catabolism or anabolism occurs. Following model development and validation with empirical data, I ran simulations and studied the responses of individuals to: (1) baseline conditions; and (2) reduced prey availability.
As expected, the baseline model accurately replicated the fluctuations in energetic requirements that result from lactating and molting seals in the wild. A 5-percent reduction in prey availability resulted in seals foraging more and resting less (from 52.2%±6.2% to 40.3±8.4% resting). At the end of the year-long simulations, animals in the baseline simulation were in significantly better condition than animals with reduced prey availability (T-test, t28=5.6, p<.0001). Our model successfully explored decision-based energy allocation strategies that occur under energetic stressors and elucidated how extrinsic conditions may impact individual fitness. Predicting the behavioral and physiological responses of top predators is a valuable contribution to the study of global change biology, and can be used to inform management decisions in Polar Regions.